Leonard Llewelyn Bulkeley Williams (2 October 1861 – 20 August 1939) was a Welsh physician and writer best known for his research on obesity and advocacy of a raw vegetarian diet.

[1] Historian Ina Zweiniger-Bargielowska has noted that Williams "linked obesity with the petty comforts of sedentary suburban middle-class life or the rampant consumerism of new wealth.

[2] He attributed most diseases including cancer to autointoxication (defective operation of the alimentary canal) and slow poisoning from constipation.

"[2] His book The Science and Art of Living, was described in a review as a "slashing attack on meat-eaters, sweet-eaters and over-eaters".

He argued that meat, sugars and starches should be replaced with fruit, raw vegetables and unsterilised dairy products.

He stated that raw fruits and vegetables are essential to health and if they are not eaten then vitamin deficiencies emerge.